1. We have isolated two complete chick collagen genes: Alpha2 type I and type III and have begun to isolate three others Alpha1 type I, type II, and type IV. Comparison of the structure of the Alpha2 type I and type III collagen gene has revealed additional information on the assembly mechanism of the ancestral gene, its amplification and the further evolution of the individual genes. Over the 200,000,000 years since their divergence, the genes for Alpha2(I) and type III have undergone little or no recombinational duplications or rearrangement of their exons except for conversions of small segments of genes. 2. Studies on methylation and DNase sensitivity of the chick Alpha2(I) collagen gene from several types of tissues with different levels of collagen synthesis suggests at least three levels of regulations for the expression of these genes. 3. We have studied the expression of the promoter region of the chick Alpha2(I) collagen gene after transfection into chick embryo fibroblast in culture with a tester gene linked to the promotor. The activity of this promoter is increased by "enhancing sequences" like those which contain the 72 bp repeat of SV40 or an analogous region in polyoma. The level of gene expression can also be increased by changing the sequences surrounding the polyA addition site.